Use more performant compression package

[101arrowz]

I've authored a compression library, FFlate, that is much more performant than Pako. It also incorporates ZIP compression, like JSZip, but compresses large files in parallel. If some of these ideas were implemented here, performance would improve dramatically. See a CodeSandbox for a comparison of JSZip, UZIP (a fast ZIP library I found), and FFlate. (Of course, the primary way to fix the abysmal performance above v3.1.5 is #702).